Mg, Ca and Ba glutaratouranylates – Synthesis and structure

Article abstract of DOI:10.1016/j.poly.2017.11.031

Three novel uranyl coordination polymers were synthesized and structurally characterized by single crystal X-ray diffraction – [Mg(H₂O)₆][UO₂(glt)(Hglt)]₂·6H₂O (1), [Ca(H₂O)₄][UO₂(glt)(Hglt)]₂·4H₂O (2) and [Ba(H₂O)₅][UO₂(glt)(Hglt)]₂·2H₂O (3), where glt = C₅H₆O₄^2? (glutarate) and Hglt = C₅H₇O₄^? (hydroglutarate) anions. The structures of compounds 1–3 contain 1D [UO₂(glt)(Hglt)]^? units that belong to the AQ⁰²B⁰¹ (A = UO₂²⁺, Q⁰² = glt, B⁰¹ = Hglt) crystallochemical group. The different roles of alkaline earth R²⁺ cations in the structures and the flexibility of the glutarate anions account for the structural distinctions of 1–3. The diverse ways for the connection between the R²⁺ ions and the [UO₂(glt)(Hglt)]^? chains, the water content and the geometry of the uranyl-glutarate units present the main structural features of the new complexes. A comparative analysis based on Pauling's second rule of 1–3 and alkali glutaratouranylates has allowed an explanation of their structural dissimilarity.

Full text of DOI:10.1016/j.poly.2017.11.031

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Mg, Ca and Ba glutaratouranylates – synthesis and structure
S.A. Novikov, L.B. Serezhkina, M.S. Grigor'ev, V.N. Serezhkin
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Please cite this article as: S.A. Novikov, L.B. Serezhkina, M.S. Grigor'ev, V.N. Serezhkin, Mg, Ca and Ba
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Mg, Ca and Ba glutaratouranylates – synthesis and structure
S.A. Novikova,1, L.B. Serezhkinaa, M.S. Grigor’evb, V.N. Serezhkina,
aSamara National Research University, 443086 Samara, Russia
bFrumkin Institute of Physical Chemistry and Electrochemistry RAS, 119991
Moscow, Russia
1 Corresponding author.
E-mail addresses: serg.alex.novikov@gmail.com (S.A. Novikov).
1

Abstract
Three novel uranyl coordination polymers were synthesized and structurally characterized by
single
crystal
X-ray
diffraction
-
[Mg(H2O)6][UO2(glt)(Hglt)]2·6H2O
(1),
[Ca(H2O)4][UO2(glt)(Hglt)]2·4H2O (2) and [Ba(H2O)5][UO2(glt)(Hglt)]2·2H2O (3), where glt =
-
C5H6O42- (glutarate) and Hglt = C5H7O4 (hydroglutarate) anions. The structures of compounds 1-
3 contain 1D [UO2(glt)(Hglt)]- units that belong to the AQ02B01 (A = UO22+, Q02 = glt, B01 = Hglt)
crystallochemical group. The different roles of alkaline earth R2+ cations in the structures and the
flexibility of the glutarate anions account for the structural distinctions of 1-3. The diverse ways
for the connection between the R2+ ions and the [UO2(glt)(Hglt)]- chains, the water content and
the geometry of the uranyl-glutarate units present the main structural features of the new
complexes. A comparative analysis based on Pauling's second rule of 1-3 and alkali
glutaratouranylates has allowed an explanation of their structural dissimilarity.
Keywords: Uranium, Coordination polymer, Glutarate
2

1. Introduction
Coordination polymers and metal-organic frameworks with the uranyl ion have been under
scrutiny over the past decade [1-3]. Utilizing a variety of O- and N-donor linkers in the
synthesis, many new structurally and topologically diverse compounds of this group have been
obtained, some of which possess notable optical properties [4-7]. The development of rational
approaches to the design of new coordination polymer materials with predetermined
dimensionality, topology and functionality remains challenging nowadays. In this connection,
the stepwise study of systems with the uranyl ion and certain linker molecules under controlled
synthetic conditions is necessary.
Anions of dicarboxylic acids are very common linkers for the synthesis of new uranium
coordination polymers. We should note that examples of dicarboxylate uranium complexes have
been reported for the first thirteen homologues of the saturated dicarboxylic acid family. The
largest structurally characterized group of dicarboxylates is the oxalate group. Crystal structures
of uranium oxalates include complexes with all possible dimensionalities and a wide topological
variety. The increase of the dicarboxylate linker length may induce the appearance of very
peculiar structures. The most remarkable examples of this peculiarity are the Borromean-type
association of 2D units in [Mn(C12H8N2)3][(UO2)2(C11H22(COO)2)3] [10] and polycatenation of
the 2D network in [UO2(C6H8O4)(C10H8N2)] [13]. The major contribution in the study of
compounds with long chain linkers (six or more carbon atoms) belongs to Thuéry's [8-11] and
Cahill's [12-15] groups.
Recently we have obtained a group of compounds with the R[UO2(glt)(Hglt)]·H2O (R+ =
Na+, K+, Rb+ or Cs+) formula which contain glutaric acid anions as linkers [16]. Herein we carry
on our comprehensive study of uranyl-glutarate coordination polymers by replacing the
monovalent cations with bivalent alkaline earth cations.
We report the synthesis and structures of three alkaline earth glutaratouranylates:
[Mg(H2O)6][UO2(glt)(Hglt)]2·6H2O (1), [Ca(H2O)4][UO2(glt) (Hglt)]2·4H2O (2) and
[Ba(H2O)5][UO2(glt)(Hglt)]2·2H2O (3). The title compounds illustrate the influence of the
incorporation of auxiliary cations on the dimensionality of the structural units in the uranyl
glutarate series.
2. Experimental
2.1 Synthesis
Uranium (VI) oxide (UO3) and commercially available glutaric acid (H2glt), calcium oxide,
magnesium and barium chlorides were all used for synthesis of 1-3 as received. UO3 was
3

obtained by the thermal decomposition of uranyl nitrate, UO2(NO3)2·6H2O, in air at 330 °C for
24 h.
Mg(UO2)2(glt)2(Hglt)2·12H2O (1)
MgCl2·6H2O (0.033 g, 0.16 mmol), UO3 (0.100 g, 0.35 mmol) and H2glt (0.185 g, 1.40
mmol) were used for the synthesis. First, glutaric acid was dissolved in 4 ml of distilled water
and then uranium oxide powder was added. The reaction was moderately heated to dissolve the
oxide, resulting in a yellow solution, which was treated with 2 ml of magnesium chloride
solution. Slow evaporation of the solution (pH ≈ 2.0) at room temperature yielded yellow
crystals of 1. Yield: 39% based on uranium. Chem. analysis, found (calculated): U 36.8%
(36.5%).
Ca(UO2)2(glt)2(Hglt)2·8H2O (2)
Crystals of 2 were obtained as follows: UO3 (0.100 g, 0.35 mmol) was mixed with an H2glt
solution (0.138 g, 1.04 mmol in 4 ml of water). CaO (0.020 g, 0.35 mmol) was added to H2glt
(0.046 g, 0.35 mmol in 2 ml of water) in a separate vial. These two solutions were combined
(resulting pH ≈ 3.0) and evaporated at room temperature. After one week, crystals of 2
precipitated. Yield: 35% based on uranium. Chem. analysis, found (calculated): U 38.0%
(38.2%).
Ba(UO2)2(glt)2(Hglt)2·7H2O (3)
The synthesis of 3 was carried out in the same way as for 1, substituting MgCl2·6H2O with
BaCl2·2H2O. Yield: 41% based on uranium. Chem. analysis, found (calculated): U 35.5%
(35.9%).
Our numerous attempts to obtain the Sr analogue of 1-3 led to poor quality crystals which
were not appropriate for XRD experiments.
2.2 Single crystal XRD
X-ray diffraction experiments were carried out using a Bruker KAPPA APEX II automated
four-circle diffractometer equipped with an area detector. The lattice parameters were refined
from all the collected reflections [17]. The experimental reflection intensities were corrected for
absorption using SADABS (for 1 and 3) software [18] and the TWINABS (for 2) program [19].
The structures were solved by direct methods (SHELXL97-2014 [20]) and refined by full-matrix
4

least squares [21] calculations against F2 in an anisotropic approximation for all non-hydrogen
atoms. The crystal structure of Ca(UO2)2(glt)2(Hglt)2·8H2O (2) was determined and refined from
a twin crystal. The components of the twin are related by 180º rotation around the a-direction,
and the contribution of the minor part is 0.2968(15).
The H atoms of the CH2 groups were placed in geometrically calculated positions with the
isotropic temperature factors being 1.2 Ueq of the C atom factors. The H atoms of the water
molecules and -COOH groups were partially located from difference Fourier syntheses and
refined isotropically with restrains on the O–H distances and H–O–H angles, and the isotropic
temperature factors being 1.5 Ueq of the O atom factors. Relevant crystallographic data for 1-3
are summarized in Table 1. The coordination numbers (CN) of the atoms were calculated by the
intersecting spheres method [22].
Table 1
Selected crystallographic data and parameters of the XRD experiments for
Mg(UO2)2(glt)2(Hglt)2·12H2O
(1),
Ca(UO2)2(glt)2(Hglt)2·8H2O
(2)
and
Ba(UO2)2(glt)2(Hglt)2·7H2O(3).
3
1
2
Chemical formula
Formula weight
Space group
a (Å)
b (Å)
c (Å)
C20H50MgO32U2
1302.96
C20H42CaO28U2
1246.68
C20H40BaO27U2
1325.93
P21/n
P21/n
P 1
8.6588(2)
9.9824(3)
11.9098(3)
105.098(2)
95.861(2)
91.646(2)
987.06(5)
2
8.2381(8)
17.6028(18)
12.8526(12)
90
97.184(6)
90
1849.2(3)
2
2.235
7.8675(2)
23.9490(6)
19.3119(5)
90
98.9550(10)
90
α (°)
β (°)
γ (°)
V (Å3)
3594.37(16)
4
Z
ρcalc (g/cm3)
2.192
8.314
2.452
10.170
µ (mm–1)
8.983
35.000
29.995
27.499
θ
max (°)
-12≤ h ≤12,
-14≤ k ≤13,
-16≤ l ≤16
-9≤ h ≤10,
-22≤ k ≤22,
-16≤ l ≤16
-12≤ h ≤12,
-31≤ k ≤38,
-27≤ l ≤31
h, k, l range
Reflections collected /
unique
Rint
12936/5684
17017/6653
81964/15801
0.0526
0.0354
1.098
0.0454
0.0336
1.018
0.1000
0.0616
1.082
R1 (I> 2σ(I)
S
Largest difference peak/hole
(e/Å3)
1.719/-1.496
1.887/-2.462
1.323/-1.701
5

3. Results and discussion
3.1. Description of the crystal structures
The structures of 1-3 contains four independent uranium atoms with CN = 8. The uranium
coordination polyhedra have the shape of a hexagonal bipyramid with shorter axial uranyl U=O
bonds, 1.761–1.785 Å, compared to the equatorial bonds, 2.426–2.513 Å, consistent with the
literature data [23,24]. In 1 and 3, the U=O distances within a single UO22+ cation differ by ≈
0.01 Å, which is likely due to the formation of hydrogen bonds involving the uranyl oxygen
2+
atoms. The UO2 ions in the discussed structures are nearly linear, with an average O=U=O
angle equal to 178.7(6)°. Each UO8 bipyramid shares two edges with two bis-bidentate glutarate
anions and one edge with a single-bidentate hydroglutarate anion.
In the structures of 1-3, the glt2- and Hglt- anions adopt Q02 and B01 types of coordination
with respect to the uranium atom (Fig. 1). Hereinafter the designation of coordination types and
crystallochemical formulae are given according to the system in reference [25]. In this system,
the general denticity of a ligand (i.e. the number of atoms involved in bonding with the metal
centers) is indicated by the capital letter. For example, the glutarate ions in 1-3 form four bonds,
which corresponds to the symbol “Q” (“quadri” = “four”). The superscript indices specify the
number of corners, edges, faces, etc. shared by the uranium atom and the ligand, i.e. 02 in this
case.
glt2- // Q02
Hglt- // B01
Fig. 1. The coordination of the glutaric acid anions to the uranyl cations in the glutaratouranylate
structures 1-3. Hereinafter, the uranium coordination polyhedra are yellow, carbon, oxygen and
hydrogen atoms are green, red and blue respectively.
6

In the considered compounds each glutarate ion links two uranyl centers to form infinite
chains enframed by bidentate hydroglutarate anions. These chains have the [UO2(glt)(Hglt)]-
composition, identical to the composition of the chains found earlier in the structures of alkali
metals (R+) glutaratouranylates [16,26]. There are two different types of [UO2(glt)(Hglt)]- units
in the glutaratouranylates structures with the R+ and R2+ (1-3) cations. The most common type is
characterized by one side placement of Hglt- anions, wherein the extent of chain distortion may
differ (Fig. 2a). The second type of chain with alternate placement of hydroglutarate ions was
revealed in the structure 2 for the first time (Fig. 2b).
a)
b)
Fig. 2. A fragment of the [UO2(glt)(Hglt)]- chain and its simplified representation in: a)
[Mg(H2O)6][UO2(glt)(Hglt)]2·6H2O (1); b) [Ca(H2O)4][UO2(glt) (Hglt)]2·4H2O (2).
7

The magnesium cations in 1 form the typical hexaaqua complex [Mg(H2O)6]2+.
Electrostatic interactions and multiply hydrogen bonds betweenthe complex magnesium counter
ion and uranyl-glutarate chains results in the formation of a 3D framework in 1.
In the second structure, the Ca2+ ion has CN = 6 and coordinates to four water molecules
and two oxygen atoms from two hydroglutarate ions, which display the M1 type of coordination
to the calcium center. Since the Hglt- anions belong to two neighboring [UO2(glt)(Hglt)]-chains,
the calcium ions draw the uranyl-glutarate chains together, with the formation of infinite
[Ca(H2O)4][UO2(glt)(Hglt)]2 layers in the bc plane (Fig. 3).
Fig. 3. A fragment of the [Ca(H2O)4][UO2(glt)(Hglt)]2 layer in the structure 2. The calcium
polyhedra are cyan.
The barium atoms in 3 have CN = 9 and form bonds with five water molecules, two
glutarate ions (with M1 coordination to the Ba atoms) and one hydroglutarate ion (with B2
coordination). Here, the formation of infinite [Ba(H2O)5][UO2(glt)(Hglt)]2 layers in the ac plane
takes place (Fig. 4). However, the increasing coordination number of R2+ leads to the formation
of denser layers, compared to those in 2.
8

Fig. 4. A fragment of the [Ba(H2O)5][UO2(glt)(Hglt)]2 layer in 3. The barium polyhedra are cyan.
Each uranyl glutarate layer in 2 and 3 participates in hydrogen bonding with the adjacent
layers and water molecules to form 3D frameworks.
3.2. Structural features of the uranyl glutarate complexes with R+ and R2+cations
Including 1-3, there are eight crystal structures with [UO2(glt)(Hglt)]- chains and R+ or
R2+counter ions reported to date (Table 2).
Table 2. Selected characteristics of uranyl glutarates with R+ and R2+ cations*
R+ / R2+ φUU,
dUU, dCC(glt), Å dCC(Hglt),
Coordination type of the Reference
anions to the R atoms
deg.
Å
Å
glt2-
-
Hglt-
M1
B2
Li
Na
K
0
9.14
4.52
5.06
5.09
5.09
4.63
4.66
[26]
[16]
48.3 9.99
45.5 10.14
T3
T3
B2
Rb
Cs
0
0
8.13
8.24
9.98
3.79
3.86
5.04
5.06
5.05
4.67
4.54
4.52
4.53
4.53
5.02
4.52
T11-8
T3
T3
-
T11-8
Mg
0
-
Ca
6.6
10.09
-
M1
M1
B2
This work
-
Ba
13.9 9.89
M1
*φUU – the angle between the equatorial planes of nearest uranyl ions in one [UO2(glt)(Hglt)]-
chain, dUU – the distance between neighbor uranium atoms in the chain, dCC – the distance
between carbon atoms of the -COO group in the given glutarate or hydroglutarate ion. Digit to
the right of the symbol of the chelate coordination type T11 shows the number of bonds in the
metallocycle formed by the given ligand.
9

The structures of the compounds with the lithium, rubidium, cesium and magnesium
cations contain uranyl glutarate chains in which the equatorial planes of the uranyl ions are
parallel (φUU = 0). The compounds with the sodium, potassium, calcium and barium cations are
built of uranyl glutarate zigzag chains. The angle between the equatorial planes of the uranyl
ions is several times higher in the compounds with Na+ and K+ (φUU ≈ 45-48о) compared to the
Са2+ and Ва2+ compounds (φUU ≈ 6-14о).
Variations of the glutaric acid anions conformation in the crystal structures can be
characterized by the dCC value, which shows the distance between the carbon atoms of the
opposite carboxylate groups in the anion. As can be seen from Table 2, dCC fluctuates more for
glutarate (3.79-5.09 Å), than for hydroglutarate (4.52-5.09 Å). The lowest dCC values of the glt2-
anions are observed in the rubidium and cesium containing structures, where glutarate anions
coordinate the R+ cations in the T11-8 mode, forming an eight-membered metallocycle (Fig. 5).
In this type of coordination, the anion binds the single R+ cation by both –COO- groups, leading
to the significant distortion of the dicarboxylate ion and a strong decrease of the corresponding
dCC value.
T3
T11-8
B2
M1
Fig. 5. The coordination types of the glutaric acid anions with respect to the R+ or R2+cations
(represented by cyan circles) in the uranyl glutarate structures.
According to Table 2, the glutarate ions in the [UO2(glt)(Hglt)]-complexes play the role of
a T3 or T11 tridentate ligand to the majority of the R+ cations (from Na to Cs). At the same time,
the four oxygen atoms of the glutarate ion are coordinated to the uranium atoms, leading to edge
10

sharing between ROn and UO8 polyhedra [16].
The structures of 1-3 differ completely from the R+ structures. The R2+ cations form bonds
with water molecules rather than glutarate anions. Thus, the magnesium cation exists as a
hexaaqua complex, the Ca atom coordinates four water molecules and Ba - five water molecules.
The magnesium ions obviously do not have any covalent bonds with the glutaric acid ions;
calcium has bonds only with Нglt-, and the barium atom coordinates to two Нglt- ions and one
glt2- ion. Therefore, U(1)O8 and BaO9 coordination polyhedra share one edge in 3.
In spite of the similar synthetic conditions for the R+ and R2+ uranyl glutarates and also the
presence of the similar[UO2(glt)(Hglt)]- chains in their structures, the nature and charge of the R
ions significantly affect the content of water in their crystals. Thus, compounds with R+ = Na, K,
Rb and Cs are monohydrates, while the Li compound includes four water molecules per formula
unit. Simultaneously, in 1-3 there are twelve, eight and seven water molecules per one R2+ ion for
Mg, Ca, and Ba, respectively. These differences of R+ and R2+ uranyl glutarates can be explained
using Pauling's second rule [27]. Each oxygen atom of the glt2- ion forms bonds with carbon and
uranium atoms. The carbon atom of the carboxyl group forms one С-С bond, so that the
remaining bond strength (sC) for each of the oxygen atoms is 3/2 valence units (v.u). The uranyl
ion forms bonds with six glutarate oxygen atoms so the bond strength of the uranyl ion is 2/6 v.u.
for each equatorial bond. Eventually, the sum of the bond strengths on each glutarate oxygen
atom (sO) is equal to sC + sU = 9/6 + 2/6 = 11/6 v.u. In the R+ compounds, where the oxygen
atoms of the glutarate ions lack δ(sO) = 1/6 v.u., the balance for the majority (3/4) of the oxygen
atoms is achieved by R-О coordination bonds. The value of δ(sO) can be decreased to 0 (R+ = Na
or K with CN = 6) or to 0.056 v.u. (R+ = Rb or Cs with CN = 9). If the oxygen atom has δ(sO) ≠
0 (for example, it has no bonding with R+), it forms hydrogen bonds with water molecules or
Нglt- ions.
In the studied R2+[UO2(glt)(Hglt)]2⋅nH2O compounds, the bond strength balance cannot be
achieved easily for the two following reasons. First, in 1-3 there are two times more oxygen
atoms with δ(sO) = 1/6 per one R2+ ion compared to the R+ compounds. Moreover, the 2+ state of
the cation changes its bond strength (sR) on each R2+-O bond to 2/6 v.u. in the case of Mg and Ca
with CN 6. In this case, only the sign (+ or -) of the imbalance could be changed, but the absolute
value would be the same. For these reasons, in 1, 2, and partially in 3, the glutarate ions do not
have bonds with the R2+cations, which form aqua complexes instead. Only in 3 do the barium
atoms with CN = 9 coordinate one glutarate-ion in a monodentate mode. As a consequence, only
one of the eight oxygen atoms has sO = 2.055 and its imbalance decreases from 0.167 to 0.055.
11

The other O atoms in 3, similar to the oxygen atoms in 1 and 2, participate in hydrogen bonding
to reduce their bond strength imbalance.
3.3. Cationic sublattice in 1-3
The mutual arrangement of the metal atoms in a crystal structure can be described by the
characteristics of their Voronoi-Dirichlet polyhedra (VDP) in the corresponding sublattice [28].
Selected parameters of the atomic VDPs in the U-sublattice of 1-3 are shown in Table 3.
Table 3. Selected parameters of atomic VDP in U-sublattice of 1-3*
VUU, Å3
493.5
462.3
469.2
429.4
CTT
Compound
Nf
18
16
14
14
dUU, Å
5.65–14.28
6.77–13.07
7.11–11.66
7.11–12.52
384264104
324652617283
445466
1
2
3
445466
*Nf is the number of U atom VDP faces, dUU is the range of distances between atoms sharing a
common VDP face, VUU is the volume of a VDP in U-sublattice, CTT is the combinatorial-
topological type of VDP (the digits are the numbers of VDP face apices, and their superscripts
are the total numbers of corresponding faces).
In the series 1-3, the number of uranium neighbors in the U-sublattice, which is determined
by the number of its VDP faces (Nf), decreases steadily from 18 to 14 simultaneously with the
growth of the R2+ ionic radius. It is noteworthy that the R+ compounds are characterized by the
opposite trend [16]. For 1-3, the shortest distance between neighbor atoms (dUU) increases. At
the same time, the VUU value fluctuates because of the changing water content and different
coordination of the R2+ cations.
According to [29], the VDP with 384264104 CTT, found in structure 1, appears to be quite
rare for uranium compounds. Polyhedra with 14 faces and 445466CTT (typical of structure 3) are
widespread and were also revealed in the Li[UO2(glt)(Hglt)]·4H2O [26] structure. The VDP with
the rarest CTT in the U-sublattice was found in 2.
It should be noted that the VDPs of the alkaline earth metal cations in the R-sublattices
have 14 faces and 4668 CTT, which is consistent with the maximum filling principle by soft
(easily deformable or intersecting) spheres [29]. The VDP of the Li atom in the corresponding
sublattice also has 4668 CTT in Li[UO2(glt)(Hglt)]·4H2O [26]. The alkali metal atoms have 16
neighbors in the R-sublattice and their VDPs relate to 3442547482 (Na and K) or 3442546284 (Rb
and Cs) CTT.
12

3.5 IR spectra
The infrared spectra of 1-3 were recorded as KBr pellets on a Perkin Elmer Spectrum 100
Fourier-transform spectrometer within the region 400–4000 cm-1. The spectra contain the
characteristic bands corresponding to the vibration of the uranyl ions, glutarate and
hydroglutarate ions, and water molecules. Assignment was done in accordance with the literature
[30,31]: ν(C=O) vibrations of COOH groups lie in a range 1693-1707 cm-1. Frequencies of
νasy(COO) vibrations are in the range 1530-1535 cm-1. Symmetrical vibrations νsym(COO) are
found in the 1404-1424 and 1453-1462 cm-1 ranges. Valence ν3 vibrations of the uranyl ions have
the following frequencies: 925 (1), 923 (2) and 923 (3) cm-1.
4. Conclusion
The
crystal
structures
of
three
novel
glutaratouranylates,
namely
(2) and
[Mg(H2O)6][UO2(glt)(Hglt)]2·6H2O
(1),
[Ca(H2O)4][UO2(glt)(Hglt)]2·4H2O
[Ba(H2O)5][UO2(glt)(Hglt)]2·2H2O (3) illustrate the different crystallochemical roles of the R2+
counter ions. In spite of the presence of similar [UO2(glt)(Hglt)]- chains in 1-3, their further
connection with R2+ cations differ significantly among the reported compounds. The counter ions
demonstrate only non-covalent interactions with the uranyl-glutarate chains in 1, while in 2 and 3
coordination of the R2+ cation by hydroglutarate and glutarate (in 3) ions appears. Moreover, the
geometry of the [UO2(glt)(Hglt)]- units in 1-3 fluctuates as a consequence of the significant
organic ions flexibility. Compared to the previously studied alkali metal complexes with the
same uranyl-glutarate structural units, compounds 1-3 contain many more water molecules per
formula unit, which can be explained in bond strength terms.
Acknowledgements
This work was performed as a part of the government assignment, supported by the
Ministry of Education and Science of the Russian Federation (project 4.5037.2017/8.9.)
X-ray diffraction experiments were performed at the Center for Shared Use of Physical
Methods of Investigation at the Frumkin Institute of Physical Chemistry and Electrochemistry,
RAS.
Appendix A. Supplementary data
CCDC 1577458-60 contain the supplementary crystallographic data for 1-3. These data
can be obtained free of charge via http://www.ccdc.cam.ac.uk/conts/retrieving.htm, or from the
13

Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: (+44)
1223 336 033; or e-mail: deposit@ccdc.cam.ac.uk.
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15

Mg, Ca and Ba glutaratouranylates – synthesis and structure, S.A. Novikov, L.B. Serezhkina, M.S.
Grigoriev, V.N. Serezhkin, Polyhedron, 2017.
Figure for content page.
2+
UO2
Ca2+
2-
-
C5H6O4 / C5H7O4

Abstract for content page
Single crystal X-ray diffraction was employed to characterize three novel
uranyl
coordination
polymers
with
glutaric
acid
anions:
[Mg(H2O)6][UO2(C5H6O4)(C5H7O4)]2·6H2O
(1),
[Ca(H2O)4][UO2(C5H6O4)
(C5H7O4)]2·4H2O (2) and [Ba(H2O)5][UO2(C5H6O4)(C5H7O4)]2·2H2O (3). Crystals
of 1-3 contain the same 1D [UO2(C5H6O4)(C5H7O4) units, but the different roles of
the alkaline earth cations significantly influence the overall structures.
17